Viruses are the etiologic cause of many life-threatening human diseases. Of special importance are herpes viruses such as herpes simplex 1 (HSV-1), herpes simplex 2 (HSV-2), cytomegalovirus (CMV), Epstein-Barr virus (EBV), varicella zoster virus (VZV) and human herpes viruses 6, 7 and 8 (HHV-6, -7 and -8) which are associated with many common viral illnesses. The HSV-1 and HSV-2 infections are characterized by cold sores of skin, mouth or genital region. After primary infection, the virus is harbored in neural cells and can reappear later in the life of a patient. Human CMV (HCMV) infection is a life-long affliction which can result in morbidity and mortality. These pathologies include microcephaly, hepatosplenomegaly, jaundice, encephalitis, infections of the newborn infants or fetuses in utero, and infections of immuno-compromised hosts. HCMV infection is responsible for retinitis, gastritis and pneumonitis in AIDS patients and HCMV-induced pneumonias or hepatitis are frequent and serious complications of organ or bone marrow transplants. EBV causes infectious mononucleosis and it is considered as the etiologic agent of nasopharyngeal cancer, immunoblastic lymphoma, Burkitt's lymphoma and hairy leukoplakia. VZV causes chicken pox and shingles. Although in children the chicken pox is usually a non-fatal disease, the recurrent form of this infection, shingles, may in advanced stage lead to paralysis, convulsions and ultimately death. Again, in immunocompromised patients the infection with VZV is a serious complication. Human herpes virus 6 (HHV-6) which is commonly associated with children's rash was also identified in acquired immunodeficiency syndrome (AIDS) patients and it may be a cofactor in the pathogenesis of AIDS in hosts infected with human immunodeficiency virus (HIV). Levine, A. J. Viruses, Ch. 4, W. H. Freeman & Co., New York, pp. 67-85 (1992); Human Herpesvirus Infections, Raven Press, New York (1986); Schirmer, E. C., et al., Proc. Natl. Acad. Sci. USA 88:5922-5926 (1992). Human herpes virus 8 (HHV-8) was identified in patients with Kaposi sarcoma, a fatal affliction accompanying AIDS. Chang, Y., et al., Science 266:1865-1869 (1994).
HIV is the underlying cause of AIDS, a world-wide epidemic with fatal consequences. According to the Joint United Nations Programme on HIV/AIDS, 40 million people are estimated to be living with HIV/AIDS at the end of 2001. During that same year, AIDS caused the deaths of an estimated 3 million people.
Hepatitis B virus (HBV) is a virus that causes chronic disease responsible for serious liver damage, including cirrhosis of the liver, cancer, organ failure and ultimately, death. It is estimated that approximately 300 million people worldwide are infected with HBV. According to the CDC, there are approximately 1.25 million Americans chronically infected with HBV. Although use of a prophylactic vaccine has reduced the incidence of new HBV infections, there continues to be a need for an effective therapeutic drug.
Various derivatives of nucleoside analogues have been found to exhibit antiviral activity. Notably, acyclovir (Zovirax) and its prodrug valacyclovir (Valtrex) are approved drugs for infections caused by HSV-1 and HSV-2. Acyclovir Therapy for Herpesvirus Infections (Baker, Ed.), M. Dekker, New York (1990); Against HCMV, four drugs are currently available: Ganciclovir (Cytovene), cidofovir (Vistide), antisense oligonucleotide fomivirsen (Vitravene) and foscarnet (Foscavir). However, only ganciclovir is effective orally but it requires large doses and produces potentially serious adverse effects such as bone marrow suppression. Ganciclovir Therapy for Cytomegalovirus Infection (Spector, S. S., Ed.), M. Dekker, New York (1991). A considerable effort went into design, synthesis and biological investigation of analogues of these drugs as well as in development of new antiviral agents. Larsson, A., et al., Antimicrob. Agents & Chemother. 30:598-605 (1986); Ashton, W. T., et al., J. Med. Chem. 31:2304-2315 (1988). Cidofovir and fomivirsen are approved only for topical application against retinitis in AIDS patients and foscarnet is used only by intravenous route and it leads to characteristic toxicity.
Current drugs for AIDS include AZT (zidovudine, Retrovir), ddI (didanosine, Videx), ddC (zalcitabine, Hivid) and d4T (stavudine, Zerit). De Clercq, E., J. Med. Chem. 38:2491-2517 (1995). Allenic nucleoside analogues such as adenallene and cytallene are examples of anti-HIV agents containing an unsaturated alkyl group. U.S. Pat. No. 4,935,427; Zemlicka, J., Allenols Derived from Nucleic Acid Bases—a New Class of Anti-HIV Agents: Chemistry and Biological Activity in Nucleosides and Nucleotides as Antitumor and Antiviral Agents (Chu, C. K.; Baker, D. C., Eds.), Plenum Press, New York, pp. 73-100 (1993). For HBV, alpha interferon and 3TC (lamivudine; Epivir) are two drugs licensed for the treatment of persons with chronic HBV infection. Unfortunately, only about 40% of patients respond to these drugs and resistance is a growing problem.
Particular 2-hydroxymethylcyclopropylidenemethylpurines and their utility against certain viruses have been described elsewhere (see, for example, co-owned U.S. Pat. No. 6,352,991; Qiu, Y. L., et al., J. Med. Chem. 41:10-23 (1998); Antiviral Chem. Chemother. 9:341-352 (1998)). However, there continues to be a need for novel compounds which are active against pathogenic viruses, including HCMV, HSV-1, HSV-2, HHV-6, HIV, and hepatitis B virus (HBV).